1. Field of the Invention
The present invention relates to an optical pick-up apparatus which reads information in an optical recording medium such as CD (Compact Disk), DVD (Digital Versatile Disk) or the like and records the information into an optical recording medium and also relates to a semiconductor laser apparatus which can be preferably implemented for the optical pick-up apparatus.
2. Description of the Related Art
FIG. 28 is a view showing simplified configuration of a conventional optical pick-up apparatus 1 and FIG. 29 is a view showing diffraction light occurring after laser lights R and r emitted from first and second semiconductor laser elements 12 and 13 respectively transmit a grating 3. In addition, in FIG. 29, a broken line is drawn respectively for first-order diffraction light R1 and first-order diffraction light R1′ occurring when the laser light R emitted from the first semiconductor laser element 12 is spectrally split by incidence of the laser light R on the grating 3 and a solid line is drawn respectively for first-order diffraction lights r1 and r1′ occurring when the laser light r emitted from the second semiconductor laser element 13 is spectrally split by incidence of the laser light r on the grating 3.
The optical pick-up apparatus 1 comprises a semiconductor laser unit 2, the grating 3 (however, there is a case where the grating is represented as diffraction grating in the following description), a collimating lens 4, a beam splitter 5, an object lens 6, a splitting element 7, a light-receiving element 8, a driving portion 9, a signal processing portion 10 and a control portion 11. The optical pick-up apparatus 1 is used for optically reading information recorded on an information recording surface of an optical recording medium 17 and for optically recording the information in the information recording surface.
The semiconductor laser unit 2 comprises the first semiconductor laser element 12 emitting red wavelength laser light whose oscillating wavelength is for instance 654 nm, the second semiconductor laser element 13 emitting infrared laser light whose oscillating wavelength is for instance 784 nm, a stem 14, leads 15 and a cap 16. The first semiconductor laser element 12 is used at the time of reading information for instance in DVD. (Digital Versatile Disk) and the second semiconductor laser element 13 is used at the time of reading information for instance in CD (Compact Disk).
In the following description, there is a case where the first semiconductor laser element is represented as a laser element for DVD and the second semiconductor laser element is represented as a laser element for CD.
In the optical pick-up apparatus 1, when the laser light R emitted from the laser element 12 for DVD is incident on the grating 3, the laser light R is spectrally split into three laser lights consisting of zero-order diffraction light R0 transmitting the grating 3 without diffraction, diffracted first-order diffraction light R1 and diffracted first-order diffraction light R1′. When the laser light r emitted from the laser element 13 for CD is incident on the grating 3, the laser light r is spectrally split into three laser lights consisting of zero-order diffraction light r0 transmitting the grating 3 without diffraction, diffracted first-order diffraction lights r1 and r1′. As mentioned above, when the laser light R and the laser light r emitted respectively from the laser element for DVD 12 and the laser element for CD 13 are incident on the grating 3, diffraction angles and diffraction efficiency are respectively different depending on difference between wavelengths of two laser lights R and r, but the two laser lights R and r are spectrally split in concurrence with each other by the grating 3.
After the laser lights R1 and r1 are spectrally split respectively into three laser lights by the grating 3, the split laser lights pass through the collimating lens 4, the beam splitter 5 and the object lens 6 and are converged on the optical recording medium 17. A substantially half of light is reflected by the beam splitter 5 and the reflected light is not used. Laser light reflected by the optical recording medium 17 passes through the object lens 6 and then a substantially half of the reflected laser light is reflected by the beam splitter 5, and the reflected light is incident on the predetermined light-receiving element 8 via the splitting element 7.
The beam splitter 5 is concretely configured by an infrared dichroic beam splitter and a red dichroic beam splitter which are arranged on a common optical axis. The infrared dichroic beam splitter has fifty percent of reflectance for the laser element 13 for CD and makes a hundred percent of incident light transmit the infrared dichroic beam splitter for the laser element 12 for DVD. In addition, the red dichroic beam splitter has fifty percent of reflectance for the laser element 12 for DVD and makes a hundred percent of incident light transmit the infrared dichroic beam splitter for the laser element 13 for CD.
On the splitting element 7, signal light is split so as to get information, a focus error signal (hereinafter abbreviated to FES) and a tracking error signal (hereinafter, abbreviated as TES) which are recorded in the optical recording medium 17.
When TES of DVD is detected, DPP (Differential Push-Pull) method is used. In this case, it is sufficient that laser light emitted from the laser element 12 for DVD is split into three portions including an optical axis through the splitting element 7 and the three portions are received. Here, as to the laser light emitted from the laser element 12 for DVD, a section perpendicular to the optical axis is circular. In addition, when FES of DVD is detected, the laser light emitted from the laser element 12 for DVD is split into a first semicircle including the optical axis and a second semicircle and the second semicircle is additionally split into two quarter circles which include the optical axis and have an equal area and thereby FES can be detected in a knife-edge method.
On the other hand, when TES of CD is detected, a three-beam method, using three laser lights which are emitted from the laser element 13 for CD and are spectrally split by the grating 3, is used. In addition, when FES of CD is detected, the zero-order diffraction light on the grating 3 is split into two portions including the optical axis by the splitting element 7 and thereby FES can be detected in the knife-edge method.
The laser light being incident on the light-receiving element 8 is converted to an electric signal. On the basis of this electric signal, Reading is performed for an information signal recorded on the information recording surface of the optical recording medium 17 such as CD and DVD or the like, and a detection of FES and TES is performed.
Here, FES is used for performing control for adjusting a focus so that the focus can be always formed on the information recording surface by following surface oscillation of the optical recording medium 17. TES is used for performing a control for correcting a gap from a track center of laser light converged on the information recording surface of the optical recording medium 17 to perform a control for making the laser light follow the track precisely.
As another prior art, an optical head which is provided with two semiconductor laser elements having different oscillating wavelength and reads out signal on the optical recording medium with different signal reading out wavelength. This optical head is provided with a polarization hologram which incident laser light transmits as zero-order diffraction light or on which the laser light is diffracted as ± first-order diffraction light in dependence on the difference in an oscillating direction of the laser light.
On the optical head, two laser lights emitted from the two semiconductor laser elements having different oscillating wavelengths concurrently transmit the polarization hologram as zero-order diffraction light, and pass through the collimating lens, a quarter-wavelength plate and the object lens and are converged on the optical recording medium. The laser light reflected by the optical recording medium follows the same optical path as an approach route and passes through the object lens, the quarter wavelength plate and the collimating lens and is incident on the polarization hologram. The laser light which is incident on the polarization hologram is diffracted as ± first-order diffraction light and is incident on a photodetector disposed at a position corresponding to the diffracting direction of the laser light (for instance, see Japanese Unexamined Patent Publication JP-A 11-174226).
As mentioned above, an optical pick-up apparatus which reads and records information into an optical recording medium such as CD and DVD or the like is configured by, for instance, a semiconductor laser apparatus with a hologram laser method. The hologram laser method is explained as follows. In a semiconductor laser apparatus for which a semiconductor laser element, a hologram element and a light-receiving element for detecting a signal are incorporated in one package, laser light is emitted from the semiconductor laser element, and a signal light reflected by the optical disk functioning as an optical recording medium is diffracted by a hologram element in a direction which is different from the semiconductor laser element traveling direction, and the signal light is guided to the light-receiving element for detecting a signal.
A semiconductor laser apparatus 100 shown in after-mentioned FIGS. 30A, 30B and 31 to 35 is known as a conventional semiconductor laser apparatus with use of the hologram laser method. FIG. 30A is a simplified perspective view showing the conventional semiconductor laser apparatus 100. FIG. 30B is a perspective view showing the semiconductor laser apparatus 100 from which a hologram element 106 is omitted. FIG. 31 is a front view showing the semiconductor laser apparatus 100. FIG. 32 is a right side view showing the semiconductor laser apparatus 100. FIG. 33 is a cross sectional view on a cross sectional line A—A in FIG. 31. FIG. 34 is a cross sectional view on a cross sectional line B—B in FIG. 31. FIG. 35 is a cross sectional view on a cross sectional line C—C in FIG. 31. Here, an X-axis, a Y-axis and a Z-axis shown in these drawings are three-dimensional orthogonal coordinate axes. Directions of the X-axis, the Y-axis and the Z-axis correspond to a longitudinal direction, a width direction and a thickness direction respectively of the semiconductor laser apparatus 100.
The semiconductor laser apparatus 100 comprises a semiconductor laser element 101, a sub-mount 102, an optical axis conversion mirror 103, the hologram element 106, a light-receiving element 107 for detecting a signal, an insulating frame 108, and leads 109. The hologram element 106 comprises a grating for generating three beams 104 and a hologram pattern 105. The sub-mount 102 is mounted on an island portion 111.
In an optical pick-up apparatus using the semiconductor laser apparatus 100, a plurality of light sources having different oscillation wavelengths are required for performing reading and writing information with the following two optical recording media. One is an optical recording medium called as CD family which performs reading and recording of information using only light, and the other is an optical recording medium called as DVD family which performs reading and recording information using light and magnetism. In the conventional semiconductor laser apparatus 100, as a light source, the semiconductor laser element 101 is applied, and the semiconductor laser element 101 comprises first oscillating point emitting a laser light for performing reading and recording for the optical recording media of CD family, and second oscillating point emitting a laser light for performing reading and recording toward the optical recording media of DVD family.
The laser lights 110a and 110b emitted from the first and the second oscillating points of the semiconductor laser element 1 respectively in the conventional semiconductor laser apparatus 100 are reflected by the optical axis conversion mirror 103 as shown in FIG. 33, and the traveling direction of the laser lights 110a and 110b is changed to vertical direction. The laser lights 110a and 110b which are changed the traveling direction by the optical axis conversion mirror 103 are incident on the grating 104 for generating three beams. When the laser lights 110a and 110b are incident on the grating 104 for generating three beams, the laser lights 110a and 110b are split into zero-order diffraction light which is transmitted without being diffracted and ± first-order diffraction light which is diffracted. After being split into three laser lights by the grating 104 for generating three beams, three laser lights are converged on an optical recording medium which is not shown in the figures. As shown in FIG. 35, the laser lights 110a and 110b emitted from the semiconductor laser element 101 and reflected by the optical recording medium, are diffracted by the hologram pattern 105, and are incident on the predetermined receiving portion of the light-receiving element 107 for detecting a signal.
When a tracking error signal (hereinafter abbreviated as TES) in the optical recording medium of CD family is detected, a three-beam method is applied in which a sub-beam proceeds in an elongating direction of the optical recording medium track against a main beam and another sub-beam follows are used. Further, when the TES in the optical recording medium of DVD family is detected, a phase difference method using the phase difference between signals splitting the main beam is used.
In another conventional semiconductor laser apparatus, a semiconductor laser chip is mounted on a chip mounting portion, a connecting point on external leads provided by surrounding the chip mounting portion and an electrode of the semiconductor laser chip are connected, and a frame body made from insulating material is provided surrounding the chip mounting portion and the connecting point on external leads. A hologram optical element including a grating pattern for generating three beams and a hologram pattern for beam splitter is mounted On the frame body. The laser light emitted from the semiconductor laser chip is split into three laser lights by the grating pattern for generating three beams, and then is converged on the optical disk. The laser light reflected by the optical disk is diffracted by the hologram pattern for beam splitter, and is incident on a light detecting circuit (for instance, see Japanese Unexamined Patent Publications JP-A 6-203403, JP-A 2000-196176, JP-A 2000-196177, and JP-A 2001-111159).
Furthermore, a semiconductor laser apparatus in another prior art, a semiconductor laser chip is mounted on a lead frame, and the lead frame is encapsulated with resin package. On the resin package, a hologram element including a grating and a hologram is mounted. Laser light emitted from a semiconductor laser chip is reflected by a micro mirror and is incident on the grating, and is split into three laser lights, then is converged on an optical disk. Laser light reflected by the optical disk is diffracted by a hologram, and is incident on a photodiode (for instance, see Japanese Unexamined Patent Publication JP-A 11-25465).
In the above mentioned conventional optical pick-up apparatus 1, when the TES of CD is detected, for instance, the three-beam method is applied. In the three-beam method, TES is detected by using three laser lights r0, r1, and r1′ to which a laser light r having infrared wavelength emitted from a laser element 13 for CD is spectrally split by the grating 3. In the optical pick-up apparatus 1, when the TES of DVD is detected, for instance, DPD (Differential Phase Detection) method is applied. In the DPD method, TES is detected by splitting light R0 which is one laser light transmitted as zero-order diffraction light by the fact that laser light R having red wavelength emitted from the laser element 12 for DVD is incident on the grading 3.
As mentioned above, the TES of DVD can be detected by only applying one laser light R0, and it is not necessary to split the laser light R emitted from the laser element 12 for DVD to three laser lights R0, R1, and R1′ by the grating 3. In other words, when the TES of DVD is detected, the grating 3 is not necessary. However, in the optical pick-up apparatus 1 having the semiconductor laser unit 2 provided with the laser element 12 for DVD and the laser element 13 for CD having different oscillating wavelength, positions on which the laser element 12 for DVD and the laser element 13 for CD are arranged are close to each other and therefore it is difficult for the optical pick-up apparatus 1 to make only laser light emitted from one laser element incident on the grating 3 and not to make laser light emitted from another laser element incident on the grating 3. This is because conventional optical pick-up apparatus 1 cannot help splitting the laser light R emitted from the laser element 12 for DVD to the three laser lights R0, R1, R1′ by grating 3.
Consequently, when TES of DVD is detected, there is usage of one laser light R0 which is not diffracted and transmits as zero-order diffraction light among laser lights R0, R1 and R1′ spectrally split by the grating 3 and there is not usage of the two laser lights R1 and R1′ spectrally split. Therefore, there is a problem that optical utilization efficiency for the laser light R emitted from the laser element 12 for DVD is reduced. In addition, there is a problem that current consumption is increased by increasing quantity of light of the laser light R emitted from the laser element 12 for DVD in consideration of lowering of the optical utilization efficiency.
As to an optical head in Japanese Unexamined Patent Publication JP-A 11l -174226, two photodetectors should be arranged on a predetermined position on which a semiconductor laser element is sandwiched between the photodetectors and therefore there is a problem that assembling and adjusting the photodetectors are difficult.
In the optical pick-up apparatus using the conventional semiconductor laser apparatus 100, in the case of detecting TES of the optical recording medium of the CD family for instance the three-beam method is used. In the three-beam method, TES is detected by using the three laser lights split by the grating 104 for generating three beams. In addition, in the optical pick-up apparatus using the conventional semiconductor laser apparatus 100, in the case of detecting TES of the optical recording medium of the DVD family for instance the phase difference method is used. In the phase difference method, one laser light transmitted as zero-order diffraction light among three laser lights split by the grating 104 is split and thereby TES is detected.
As mentioned above, when TES of the optical recording medium of the DVD family is detected, there is usage of one laser light which is not diffracted and transmits as zero-order diffraction light among three laser lights split by the grating 104 and there is not usage of the remaining two laser lights split. Therefore, there is a problem that quantity of light of laser light to be originally converged on the optical recording medium is reduced and thereby loss of the quantity of light arises and optical utilization efficiency for the laser light emitted from the semiconductor laser element 1 is reduced.